    Patent Literature 1: JP 2012-093506 A (US 2012/0099032 A1)    Patent Literature 2: JP 2009-196630 A (US 2009/0189753 A1)
There are conventionally known head-up displays (HUDs) which project light on a windshield or combiner in vehicles and display pictures such as an alarm to permit drivers to view them (refer to Patent Literature 1). One technology of the HUDs acquires information on an obstacle close to a host vehicle, and displays a picture to permit a gaze of a driver to view the obstacle on which the picture is superimposed (refer to Patent Literature 2).